[en] A new fatigue test apparatus was developed for the purpose of performing well-defined tests in the application of structural materials at very high temperatures in precisely controlled chemical environments. Reviewing critically the two earlier exploratory attempts of designing, constructing and testing in simulated VHTR coolant environment, a modified design philosophy was established. In the latter particular care was taken to avoid unnecessary reactions of the machine's structural components and/or outgassing from any of the instruments or sealing. To fulfill such requirements, the apparatus was given the following features; 1) Hot portion is limited to the specimen only by employing induction heating with properly designed coils so that unexpected consumption of the impurities in the helium environment is prevented. 2) LVDT (Linear Variable Differential Transformer) is sealed with stainless steel and all gaskets used are of OFHC copper so that any undesirable outgassing is avoided. 3) Through those modifications tests both in vacuum of 10^-₉ Torr and in helium with very closely controlled impurity chemistry have been made possible. 4) An automatic data acquisition system with a computer is attached for accumulation of data throughout the test period, their analysis and display. Some preliminary test results are demonstrated to justify the design methodology employed. (author)